This invention relates to a method of manufacturing a cam shaft for driving intake/suction valves in an internal combustion engine of automobiles, motor cycles, etc. and a device used therein.
In the internal internal combustion engine of an automobile, etc. cam shafts are used to open/close valves in intake/suction systems of cylinders with predetermined timing.
These cam shafts were heretofore manufactured by a casting or forging process which formed a cam, a journal, and a shaft integrally. These cam shafts were therefore inevitably heavy in weight, thus presenting a bottleneck in efforts to reduce overall engine weight. In order to overcome the problem, there has been proposed a manufacturing device which is characterized in that engaging projection/recess members are provided oppositely in order to determine the angle of each cam member so that the cam member can be manufactured to have a predetermined angular relation (Japanese patent application laid-open Sho 51-5415). In the proposed process, a hollow pipe which is a material of a shaft member is attached on the outside thereof with a cam member, and is fixed therewith by the bulging process. The engaging projection/recess members are provided on respective cam members as well as on at least the lower die of the split dies which are used for holding the cam member and for the bulging process.
However, the above device is disadvantageous in that it requires specific split dies with engaging members, and the structure of a split die is extremely complicated. Further, as different types of engines require dedicated split dies, different split dies have to be prepared especially for all the models, to thereby push up the cost.
There has also been known another method which can position a cam member by fitting a hollow shaft material which is shaped like a prism with a regular polygonal section into a square hole of the cam member, the square hole of a cam member being bored in advance at a predetermined phase angle (Utility Model Publication Sho 53-7130).
However, the cam members had to be bored to have the square holes with an extremely high precision in the proposed process to thereby present difficulties in the manufacturing process.